The present invention relates to a photographic method for forming a metal pattern on a substrate and to a photosensitive material useful therein. While the invention encompasses the formation of metal patterns for any purpose including decorative purposes, it particularly relates to the formation of electric circuits.
Commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,846 disclose an imaging system which utilizes microcapsules containing a photosensitive composition and a color precursor to form images by controlling the release of the color precursor from the microcapsules. In accordance with one embodiment of the present invention, this technology is adopted to form metal patterns and, more particularly, printed circuits.
Various methods for manufacturing printed circuits are known in the art. These methods include so-called additive, semi-additive and subtractive processes. There has been significant interest in the additive process which involves forming a pattern of a material which functions as a catalyst or nucleation site onto which the metal pattern is deposited from an electroless plating solution. Both photographic and printing techniques have been used to form these catalytic patterns. For example, inks based on resins (e.g., epoxy and polyimide resins) containing iron or nickel metal powders have been silk screened on insulative substrates and immersed in copper sulfate solutions to form copper patterns (C&E News, July 2, 1984, p.5).
U.S. Pat. No. 3,950,570 to Western Electric discloses a process in which an insulative member is coated with a photosensitive sensitizer (a colloid of a sensitizing species of Ni, Mn, U, Mo or W). By exposing the sensitizer, it is either activated or inactivated in terms of its ability to reduce an activating metal ion such as silver, palladium or platinum ion. By exposing the sensitizer in a pattern conforming to the electrical circuit and treating with a solution of the activating metal ion and then with an electroless plating solution which is catalyzed by the reduced silver, palladium or platinum, a circuit is formed. Related methods are described in U.S. Pat. Nos. 4,084,023 and 3,904,783.